This invention relates generally to threshing and more particularly to threshing machines having a rethresher cylinder of the rasp type.
While the terms "grain", "straw", and "tailings" are used principally throughout this specification for convenience, it should be understood that these terms are not intended to be limiting. Thus "grain" refers to that part of the crop material which is threshed and separated from the discardable part of the crop material which is referred to as "straw". Incompletely threshed ears are referred to as "tailings". Also, the terms "forward", "rearward", "left", "right", etc. when cited in connection with the combine harvester and/or components thereof are determined with reference to the forward operative travel of the combine harvester in the field and should not be understood to be limiting.
In known combine harvesters, grain is threshed and separated in a threshing and separating mechanism and the separated grain, together with impurities of all sorts, such as chaff, dust, straw particles, tailings, is fed to a cleaning mechanism for cleaning. Clean grain is collected and fed to a graintank for temporary storage. The tailings are separated from the clean grain and impurities for reprocessing. This reprocessing either means recycling the tailings through the threshing and separating mechanism or treating them in a separate tailings rethreshing means. In both cases the tailings are conveyed through an elevator which usually is of the paddle type.
In combine harvesters, independent tailings rethreshers have been provided which are normally arranged to receive the tailings from the cleaning mechanism and to discharge the rethreshed tailings onto the grain pan of said cleaning mechanism for recycling the tailings therethrough. This arrangement is advantageous in as far as the main threshing and separating mechanism can be used to its full capacity without any risks for unevenly loading or overloading it with tailings. These separate tailings rethreshers have proven to be advantageous especially in combination with high capacity combine harvesters since they enable components to operate with a maximum efficiency.
Nevertheless, these separate tailings rethreshers also have some limitations, one of the major ones thereof being that certain embodiments are complicated and hence expensive. One such embodiment combines a conventional type elevator with rethresher means. Another embodiment combines rethresher means with a vertical auger for feeding the tailings to the rethresher on top thereof. This structure is driven via a drive transmission including conical gears which add to the expense. In the latter arrangement tailings are not forcefully moved through the entire length of the tailings rethreshing means in the rethresher and hence a certain percentage of tailings is discharged from the rethresher prematurely, whereby these tailings once again have to pass through the rethresher after separation in the cleaning mechanism.
All known tailings rethreshers comprise a rotor cooperable with a stationary elements to rethresh the tailings on the one hand, and operable to discharge the rethreshed tailings and spread them substantially evenly over the grain pan on the other hand. Therefore the design of the rotor is a compromise to fulfil both functions to an acceptacle degree. In operation, the rotor moves the tailings over an aggressive surface thereby effecting rethreshing. The aggressive surface in some of the known tailings rethreshers extend only over a small arc so as to accommodate an inlet and an outlet opening. Thus the efficiency of such a rethresher is relatively low. In other arrangements, the aggressive surface is larger but, as already explained above, the rotor is incapable of moving all of the tailings over the entire surface, whereby the maximum efficiency is not realized.
Another limitation is that the tailings are supplied to the tailings rethresher rotor, either co-axially or in a direction generally parallel to the rotor axis. Thus the tailings are not evenly spread over the entire width of the rethreshing rotor and the associated aggressive surface which again reduces the efficiency. Also, such tailings rethreshers are unable to handle difficult crops such as wet and weed infested crops as well as crops mixed with wet sticky soil. Indeed, in these conditions crop material does no longer fluently enter between the adjacent rotor flights or paddles but instead thereof said material tends to stick in the inlet area of the rethresher as well as in the free spaces between the adjacent paddles of the rethresher rotor. This cause the capacity and the efficiency of the rethresher to drop considerably and eventually plugging may occur.
The foregoing illustrates limitations of the known prior art. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations as set forth above.